Clinical and epidemiological data implicate papillomaviruses in the etiology of certain squamous epithelial tumors in humans. Research on human papillomaviruses (HPV) has been hindered by the lack of culture systems capable of supporting vegetative viral growth. The development of an in vitro system to study HPV expression is complicated by the fact that HPV gene expression is tightly linked to the in vivo program of differentiation of squamous epithelia cells and it has been extremely difficult to mimic this program in vitro. Endogenous factors utilized to control differential gene expression in these epithelia are undoubtedly involved in the tissue tropism and regulation of HPV expression. To date, these host factors, coupled with regulatory mechanisms present within viral genomes themselves have hindered attempts to observe pathological effects of HPV gene expression in squamous epithelia in transgenic mice. These restrictions on utilization of the transgenic mouse model could be overcome with the ability to specifically target HPV gene expression to squamous epithelia. Preliminary evidence is presented in this proposal documenting the feasibility of targeting gene expression to the epidermis of transgenic mice by the use of regulatory sequences of a keratin gene which is expressed exclusively in the epidermis at a late stage of development and in cells with proliferative potential. Through the use of this unique targeting ability, an attempt will be made to determine if there are inherent differences in the early regions of HPV 6 and HPV 16 which are associated with the production of benign and malignant lesions, respectively. The effect of expression of individual early genes from HPV 6 and 16 (E5, E6, E7) on the proliferation and differentiation states of epidermal cells will also be determined. The availability of strains of mice expressing individual early genes will allow mating experiments that will determine if these genes act synergistically with each other during different stages of carcinogenesis or with other oncogenes which have previously been shown to cooperate in the malignant transformation of mouse epidermal cells. Due to the accessibility of the epidermis, it will also be possible to assess the potential role of chemical and physical carcinogens as well as tumor promoters in this process. An attempt will be made to establish a cell line capable of supporting vegetative viral growth by targeting the expression of genes with immortalizing potential with regulatory sequences expressed at a late stage of squamous differentiation. Finally, expression constructs will be developed that will allow targeting of HPV gene expression to other squamous epithelia.